Initial version of beautifying code editors

Here's the initial version of the code beautifier. Beautifies HTML, CSS, & JS - but none of their preprocessor cousins. ( From issue #341 )

It functions, but lacks two important features:

1. **Hot-keys** - I'm probably just being stupid as to why it doesn't work
2. **Beautify settings** - Wasn't sure how you wanted to store them with the rest of the settings and how to display that to people

Should probably also minify the beautifier files.

I tried to copy tern's implementation as much as possible and keep code style conventions.

I'm gonna keep working on (1) but I think (2) might be an implementation detail you guys will want to handle.
Worth double checking that `getCode` isn't a Promise. I've got a feeling it isn't, because it's just returning the buffer on CodeMirror, but worth the sanity check.